Mr. Norris, for all the good that sunscreens do, I hear there are two big negatives. Is it true that some sunscreens contain harmful chemicals? And do sunscreens block vitamin D production? – “Sensitive Skin in the Sunshine State”

With July being UV Safety Month and the pinnacle of summer sun fun, there’s no better subject to address than this one right now.

Since 1994, skin cancers have increased 300 percent, according to a study in the Archives of Dermatology. They have become the most common global cancer, with more annual cases than prostate, breast, lung and colon cancers combined, according to a treatise at SantaCruz.com.

Last week, I discussed some surprising links and causes of skin cancers outside of unprotected overexposure to the sun. They included organ transplants, medicines for autoimmune diseases and Parkinson’s disease and contact with certain chemicals, including arsenic and some pesticides.

Whatever the causes of skin cancers, it’s preventing them that should be our goal. And it all starts with minimizing exposure to all the things mentioned above that can cause or exacerbate skin cancers.

Most of all, avoid prolonged exposure to intense sunlight, especially between 10 a.m. and 4 p.m., when it’s at its peak. Don’t use sunscreen as a justification for staying out in the sun for a long time.

Even with a sun protection factor of 30, sunscreen, according to the American Cancer Society, “doesn’t protect from all UV rays.” SPF 15 blocks 93 percent. SPF 30 blocks 97 percent. And SPF 50 blocks 98 percent, according to a CNN report.

And remember that sunscreens protect only against ultraviolet radiation of relatively short wavelengths (ultraviolet B rays), not ultraviolet radiation of relatively long wavelengths (ultraviolet A rays).

Dr. Ariel Ostad, a clinical assistant professor in the department of dermatology at New York University Medical Center, explained, “Evidence has shown the best sunscreens are the ones that block UVB and UVA.”

That is why Ostad and other experts recommend using products that are labeled “broad spectrum,” meaning they protect against both UVB rays, which cause sunburns, and UVA radiation, which causes premature skin damage and aging.

That is another great reason for wearing the right sunscreen, at least on the most susceptible parts of the body; it can slow skin aging. A four-year Australian study released in early June was conducted upon a group of 900 adults, ages 25-55. It discovered that a daily dollop of sunscreen resulted in 24 percent less skin aging (wrinkling).

One last bit of caution about sunscreens: Make sure it is oxybenzone-free. Oxybenzone, which is used in 56 percent of sunscreens – as well as many cosmetics, lip balms and moisturizers – is a chemical linked to hormone disruption and babies having low birth weight. Despite the fact that the Food and Drug Administration has approved oxybenzone in sunscreen for use on children older than 6 months, oxybenzone also can release free radicals to sun-exposed skin, which leads to cell damage and skin cancers, essentially canceling the very purpose of the sunscreen to which it is added, according to the Environmental Working Group and toxicology experts.

The Environmental Working Group adds similar warnings for the chemical ingredient retinyl palmitate – a synthetic form of vitamin A found in about 25 percent of sunscreens – and issues a “low hazard” caution for the ingredient octocrylene, too.

That is why skin specialists – including Jennalee Dahlen, esthetician at Santa Cruz Skin Solutions – recommend the most natural of sunscreens, such as “good old mineral-based sunscreens containing zinc oxide or titanium dioxide … (products such as) Badger, BurnOut, Jason and the Hungarian brand Eminence.”

There’s one more important issue related to sunscreen that needs to be addressed here: Do sunscreens prevent the production of vitamin D, which is so critical to our diet?

The New York Times reported on the issue: “Yes. Studies have found that by blocking ultraviolet rays, sunscreen limits the vitamin D we produce. But the question is to what extent.”

The fact is that most clinical studies reveal that the limitations are negligible because most people generally don’t apply enough sunscreen to maximize its full impact, according to Dr. Henry Lim, chairman of dermatology at the Henry Ford Hospital and a spokesman for the American Academy of Dermatology.

New research conducted by professor Antony Young of the St John’s Institute of Dermatology at King’s College London showed that sunscreens don’t erase vitamin D production. As I noted above, no sunscreen offers 100 percent protection. And if a sunscreen isn’t broad-spectrum, UVA radiation still can reach our skin and stimulate vitamin D production.

According to the National Institutes of Health, it takes as little as 30 minutes of daytime exposure to the sunlight (without sunscreen) twice weekly to produce adequate amounts of vitamin D.

Lim recommends that people consume more foods rich in vitamin D, such as eggs, fortified milk and cereals, salmon, shrimp, sardines and cod – as opposed to not applying sunscreen.

Another idea is to take vitamin D supplements on hot summer days, when the weather warrants greater surpluses of sunscreen on our skin.

The chief of surgery at Skin & Cancer Foundation Inc., Greg Goodman, recently told the Sydney Morning Herald that he recommends that sunbathers who use sunscreens take a 1,000-unit vitamin D capsule daily to keep their levels in check – especially during the winter, when it’s likely that 90 percent of us are deficient of the nutrient.

Next week, I will discuss other surprising things – including foods – that can help prevent skin cancers.